sandblasting

[bscofield]

Would one of you experienced sandblasters consider writing a tutorial for the site? No offense to Tyler's short tutorial but he knows it was just a short blurb until he could get something else posted. I just got given to me a 125 PSI, 4 gallon compressor that I would like to make use of. So here are the questions I have:

1-) How do you protect your hands?

2-)What do you blast with? Tyler mentioned a few different things but I wondered the difference in result and price.

3-)What's a good idea for collecting and re-using the blast material?

4-)What about blasting and growth rings? Are they softer and therefore come through on their own (to a degree) or does one have to make an effort to show these?

5-)What type of gun should I be getting?


If there any other questions that you would expect someone who knows nothing about blasting to have asked, then please answer those as well.

Thanks again guys!

[KurtHuhn]

Would one of you experienced sandblasters consider writing a tutorial for the site? No offense to Tyler's short tutorial but he knows it was just a short blurb until he could get something else posted. I just got given to me a 125 PSI, 4 gallon compressor that I would like to make use of. So here are the questions I have:

That 4 gallon compressor might not be enough - unless it has one hell of a pump attached to it. Generally speaking, look at the SCFM rating at about 90 PSI. Unless it's pretty darn high (13CFM) you'll need to get very creative. I'm not going to say you *can't* sandblast with that compressor, but it will definitely need some creative thoguht - or loads of patience.

1-) How do you protect your hands?</quote>

Most blasting should take place in a blast cabinet, to cut down on the dust. Blast cabinets typically come with a set of thick gloves that simultaneously protect your hands, and make it nigh impossible to hold onto your work.

3-)What's a good idea for collecting and re-using the blast material?

Blast cabinets usually have a reservoir at the bottom that collects the media. On some of these, this is where the feed tuve gets stuck to immediately reuse the media. On others, it's just a place to hold the used media until you empty it.

4-)What about blasting and growth rings? Are they softer and therefore come through on their own (to a degree) or does one have to make an effort to show these?

The jury is still out on that one. It's all an effort. One that I will be undertaking in a week or two - bank account willing.

5-)What type of gun should I be getting?

Most blast cabinets come with one, and most pressurized hoppers also come with one. Try to get one that matches the capabilities of your compressor - as far as SCFM ratings.

That brings up a point, I've recently seen bottle blasters coming down in price. These are inexpensive sandblasters that have their reservoir in pressurized bottle, and the gun is shaped like a pencil. The rating for these is usually in the .5 to 1.5 SCFM range, and usually use 220 grit media. However, I have no idea how effective they would be with briar - they're usually used for etching glass or metal.

[JHowell]

I will state, having tried to blast with a 15 gallon compressor, that a 4 gallon is useless for sandblasting. Not that you couldn't get a $100 cabinet/gun from Harbor Freight (what I have, actually) and give it a whirl, but I think you'll find it inadequate. I agree with the rest of Kurt's assessment.

As far as compressor tank size being irrelevant, I disagree, based on my recent shopping and research. In the first place, tank size normally correllates with pump output. For general use there's no point in putting a huge pump on a tiny reservoir, and, with the exception of some gasoline-powered construction site compressors, I have yet to see an example. Likewise, there's no point in putting a tiny pump on a huge tank. One might properly caution against buying a unit like the latter, but I haven't seen one offered for sale. Manufacturers seem to match pump to tank fairly appropriately. You will see some variation in pump size/power once you get in the 60-80 gallon range -- I've seen 60-gal 2-stage units that put out 20cfm at 90psi, and 80-gal ones that put out 15. Either will work, IMO. You can, of course, buy compressor heads, motors, and tanks separately and make whatever kind of compressor you want, but the commercially available ones are as I describe. The biggest break in output is between single- and twin-stage pumps. They generally break down into the 60-gallon single stage, 5-7hp,10-12 cfm/90psi, $4-500 class, smaller than which is not useful; the 60-80 gallon twin stage 5-7hp, 14-17 cfm/90psi $800-1000 class, and the the 80-gallon, twin stage, 7-9 hp, 20+ cfm/90psi $1500-1800 class. There is at least one 60-gal twin-stage unit with a 7.5hp motor and an output around 20cfm at 90psi -- maybe an Ingersoll-Rand.

Also, typically the tank holds higher pressure than is used in the line. In my case, the 80-gal tank holds 175psi at full charge, while I use 100 or less to the blaster. That differential means I can blast for some time before the pump comes on (and the pump catches up and stops while I'm still blasting). While blasting continuously is optimal, I would guess that some makers make do with smaller compressors by blasting until the pressure drops, letting the pump catch up, then blasting again. Time-consuming, but possible. In such a case, the volume of the tank is not irrelevant. Given a big enough tank, high enough starting pressure, and enough patience, blasting could be done with an inadequate pump. My small compressor didn't work because a high enough pressure couldn't be maintained -- after about ten seconds of blasting the pressure would fall below 80psi and the pump couldn't keep up. I blasted a couple of pipes that way, but that 10-second window just wasn't enough.

Sorry for the length.

[KurtHuhn]

I'm currently shopping around for a compressor, and it's pretty much as you describe, Jack.

I'm trying to find something affordable in the 60-80gal range that uses 115V. Fat chance, I think. All the ones at Lowes seem to require 240V - at least according to the website.

[KurtHuhn]

I'm not interested in getting into an argument with you two about compressors. If you are going to purchase an already-configred rig then you have more or less figured out how to choose one based on what the manufacturers do to sell to the mass market. If you are going to build your own from components you need to understand what is going on. Nuff sed.

Random, FWIW, I agree with your assessment - to a point. If you have a beefy compressor, your reservoir size is *almost* not an issue. However, If I were to build my own compressor, I'd still go for a 60-80 gal reservoir with a 10-20 SCFM pump. That's because the large reservoir will allow me the luxury of not having the pump run continuously. It's mostly an ear comfort thing.

[Paul_Tatum]

Regarding compressor companies, I would like to share my experience with Ingersol Rand. I bought my compressor 2 years ago, more or less, and last summer the 5 hp motor went out. Come to find out it was bad from the beginning and was just limping along from the start. I understand that this sort of thing happens from time to time and am not knocking the motor.
What really impressed me though, is that I called the company customer service line and they talked me through a couple of fixes, none of which worked. After about 30 minutes of double checking everything they said they'd send me a new motor. It was on my doorstep THE NEXT DAY! We're talking about a $600, 75 lb (with packaging) item that was shipped UPS next day air at no charge to me. They said all they wanted in return was the sticker on the original motor with the serial number, and that I could do what I wanted to with the original and even suggested seeing if it could be reparied. I checked into it and it cost me $50 to have some components replaced and now I have a spare motor in my basement.

So, that's my experience with IR, and I'm happy with not only the compressor but also the service that backs it up.

My two cents on the size of the compressor, should one be looking for a new one, is that it should pump a minimum of 90psi and 15 cfm continuously. That is what mine does and it is just barely enough. Sometimes I like to blast at 120 psi for a little while and it gets difficult having to wait for the compressor to catch up.

Paul

[JHowell]

I'm not interested in getting into an argument with you two about compressors. If you are going to purchase an already-configred rig then you have more or less figured out how to choose one based on what the manufacturers do to sell to the mass market. If you are going to build your own from components you need to understand what is going on. Nuff sed.

And *I'm* not going to get into an argument with you about why anyone would bother to purchase the components separately when you can buy a well-engineered "mass market" compressor so reasonably. Or why anyone, should they choose to buy components, would put a big pump with a tank that didn't give a bit of cushion. Your argument seems to be that if you have a big enough pump you don't really need a reservoir, which, while true, seems to be truly irrelevant. Or perhaps your statement is a caution against buying a compressor with an 80-gal tank that doesn't put out enough cfm to blast. As far as I can tell, unless you insist on buying components and putting it together yourself, such a compressor doesn't exist. If you have a special need, buy components. I think the "mass market" offerings have us pipemakers pretty well covered.

In summary, if we're talking about a compressor that you can plug 'n' play, tank size is relevant. If we're talking about some Frankenstein rig using an old propane tank and a Volkswagen motor, well, then you have to know what you're doing. ; )

And Kurt, 240v is a good thing. You can probably run the line yourself -- it's not hard, other than dealing with the 8 awg wire they tell you to use.

[KurtHuhn]

And Kurt, 240v is a good thing. You can probably run the line yourself -- it's not hard, other than dealing with the 8 awg wire they tell you to use.

I need to ask my father-in-law to come over here and take a look. I could probably do it, but I'd rather an electrician supervize.

I'm thinking that I'll go for the 60-gal high-flow unit at Lowes. I need to get down there and look them all over before I pull the trigger though.

How do you like your Harbor Freight blast cabinet, Jack? I'm considering getting one from them, but don't want to get a crappy cabinet.

[KurtHuhn]

There are basically two reasons for having a reservoir. One is to even the pressure since a compressor is a reciprocating device with valves it "puffs". The other reason is to handle duty-cycle. If you have a rig with a 100% duty cycle that means it can run continuously until the cows come home, and you need only a tiny reservoir to even the air pressure.

That and reducing the amount of electricity consumption, and saving my ears. I'm not going to say you're wrong, technically, you're right. However, it is my opinion that a "proper" air compressor system shouldn't run continuously just to keep up with the demands of tools that consume a relatively small amount of air.

Most rigs you'll find at Lowe's or Home Depot have a 40-60% duty cycle, which means that if they run more than 40-60% of the time you're putting the driving motor at risk of burning out.

While that is true of the smaller rigs, the 60 and 80 gallon rigs at Lowes are rated at 100%.

[JHowell]

Maybe I'll write a report on the experience, I have no doubt that I'm way out of touch with the prices of used components. The last home-built system I worked with was a long time ago, a huge DeVilBiss V-block industrial compressor, I forget now whether it had 2 or 4 cylinders but it was really cheap and only needed a little work. I'll try and keep my mouth shut about sandblasting, you guys seem quite happy with the equipment that is being offered in the retail market.

It would be instructive to hear about such a compressor. I have heard of rigs with a tank from here for free and a motor from a seized-up conveyor belt over there for $25 and such, but I doubt that we can all count on such luck. The retail market is not, in this context, a bad thing. While a compressor certainly is the most expensive part of a blasting rig, I don't think it has to cost two thousand bucks -- mine was less than a thousand, delivered, and I'm happy with it. I might be happier still if I'd gotten a $2000 one, but this works, I could just barely afford it, and now I can blast pipes at home. It is rated for 100% duty cycle.

I agree with your air compressor design theory in general, Random. A big tank is useful for use with a big pump not just for smoothing out the piston pulses, but providing a buffer for intermittent use. You don't want those heavy startup loads every time you hit the trigger. You have quite a bit of intermittent use with blasting -- blast, wait for the dust to clear, look; blast, wait for the dust to clear, look . . .

Kurt, I think I remember looking at the Lowe's unit -- Black Max, something like that? If it's 2-stage I think it's all right, but I believe the HD biggest has slightly higher output and is a little less expensive. The thing to remember, too, is that we aren't really pushing these compressors all that hard. Even if you blast for 2 hours without stopping, that's probably a good thing, get all the moisture out of the crankcase. When I used my friend's 60-gal single-stage (10 cfm/90psi) it worked. The blasted pipes were as nice as the ones I'm doing now, I just had to wait for the compressor to catch up from time to time, and it never stopped running. That made me uncomfortable, not because I thought the compressor would die, but because, well, it wasn't mine.

As far as the HF cabinet is concerned, it's crap -- compared with much more expensive units. Compared to no cabinet at all, it's brilliant. You need the internal lights, and you need to hook a dedicated shop vac (small) to the exhaust to collect dust with a coupler with some holes in it to attenuate the suction. Mine has the back cut out and a plastic wastub attached with silicone to give a little more working room. Ideally, I'd have one of the big steel cabinets with the elbow-length gloves and a foot trigger and lots of different ceramic nozzles available, but in reality I'll probably wind up with another one of these if I need to replace it for some reason. If nothing else, it does a good job with the compressor I have. A bigger cabinet might come with a gun that needs even more air. In fact, if I ever wind up with more room for a shop I'll probably get a couple more so that I can switch media without having to, uh, switch media.

[KurtHuhn]

Kurt, I think I remember looking at the Lowe's unit -- Black Max, something like that? If it's 2-stage I think it's all right, but I believe the HD biggest has slightly higher output and is a little less expensive. The thing to remember, too, is that we aren't really pushing these compressors all that hard. Even if you blast for 2 hours without stopping, that's probably a good thing, get all the moisture out of the crankcase. When I used my friend's 60-gal single-stage (10 cfm/90psi) it worked. The blasted pipes were as nice as the ones I'm doing now, I just had to wait for the compressor to catch up from time to time, and it never stopped running. That made me uncomfortable, not because I thought the compressor would die, but because, well, it wasn't mine.

I'm somewhat tied to Lowes at the moment, since that's where all my gift cards are from. However, Lowes and Home Depot both carry Campbell Hausfeld in this area - the Home Depot just rebrands them Husky or something. I guess it doesn't make a huge difference here. I'd love to go for the 80-gal 2-stage unit, but that would completely blow the budget.

My wife wants to know why I can't get one of those little pancake compressors. 8O

[JHowell]

I'm somewhat tied to Lowes at the moment, since that's where all my gift cards are from. However, Lowes and Home Depot both carry Campbell Hausfeld in this area - the Home Depot just rebrands them Husky or something. I guess it doesn't make a huge difference here. I'd love to go for the 80-gal 2-stage unit, but that would completely blow the budget.

My wife wants to know why I can't get one of those little pancake compressors. 8O

You know the saying, when you buy a good tool, you cry only once. I waited a year before I could buy my compressor -- I'd get close, then have to buy briar, or rod, or fix the car. The gift cards won't go stale, and they won't get spent on groceries; it might be worth thinking about to sell a few more rusticated pipes and get the big boy later. I'm not sure if the models are exactly the same, but the 60-gal single stage C-H compressor is what my friend has, so I've used both compressors with the same cabinet. IMO, the 2-stage is worth the extra money. It's far better for blasting, and it runs more quietly. Not to lecture; I almost bought the 60-gal myself several times. But I'm glad I waited.

[JHowell]

Although the compressor is the heart of a sandblasting rig, the gun is really a primary determinant. The compressor needs to supply only enough air to feed the gun. I think that selecting the gun first is probably the best way to go, and I think it's an aspect that has received too little attention. The blast cabinet I had (since given to a friend) came with a cheapie gun, no specs whatsoever. "Now you have a blasting gun, good luck sucker!"

I'm not sure who makes decent blasting guns, what their prices are, where their CFM ratings commonly range. It seems goofy that what in reality is one of the most critical components of the system is so unexamined.

Just food for thought.

I think it's even more elemental than that: the nozzle. The siphon "gun" is just a valve that shoots air past a tube, creating suction that picks up media through a hose and shoots it through the nozzle at the workpiece. You could probably make one yourself, and I've been tempted to do just that if I can find a cheap foot-operated valve. I think with a siphon you're constrained by the media. If you want to reduce air consumption you have to reduce the airflow, and to do that and still create enough suction to pick up the media you have to reduce the tubing diameter, which at some point causes the media to clog. There are little pressurized spot-blasting guns which use much less air, but also hold relatively little media. You'd need a cabinet lots bigger than mine to use one, since they're much more bulky than a siphon gun, but you could always build a cabinet out of plywood.